SSLTrack::setLengthIfUnknown PHP Method

    protected function setLengthIfUnknown()
    {
        if (!isset($this->length)) {
            $this->length = $this->guessLengthFromFile();
        }
    }

 /**
  * This version of setLengthIfUnknown() looks in the cache that the track was
  * constructed with for a track with the same row ID. If it finds one, it 
  * inquired if this (possibly expensive) question has already been answered.
  * If it has, we use the answer from the cache.
  * 
  * If no answer is found in the cache, we fall back to scanning the file with
  * getID3 in the usual way. If results are found we are sure to poke them 
  * back in to the cache.
  * 
  * This is necessary because ScratchLive! can create several objects for the
  * same row (as it will write multiple, updated, versions of the row to the
  * history file over time). Several of these may be missing expensive info,
  * so we want to cache it from object to object.
  * 
  */
 public function setLengthIfUnknown()
 {
     if (!isset($this->length)) {
         // have a go at pulling it from the cache, if it's in the cache!
         $cached_track = $this->track_cache->getByRow($this->getRow());
         if ($cached_track) {
             $cached_length = $cached_track->getLength();
             if (isset($cached_length)) {
                 $this->length = $cached_length;
             }
         }
         parent::setLengthIfUnknown();
         // save in the cache, for next time.
         if (isset($this->length)) {
             if (isset($cached_track)) {
                 $cached_track->length = $this->length;
             } else {
                 $this->track_cache->register($this);
             }
         }
     }
 }